Optical system for scanning microscope

ABSTRACT

An optical system for a scanning probe microscope provides both an optical on-axis view and an optical oblique view of the sample by means of two optical paths each providing an image to a CCD camera via an auto-zoom lens. A shutter alternately blocks the image of either view from reaching the auto-zoom lens. The CCD camera provides the optical image to a video display which also displays the scanning probe image, thus eliminating the need for eyepieces and allowing easy viewing of both the optical and scanning probe images simultaneously.

RELATIONSHIP TO COPENDING APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/561,448, filed Apr. 28, 2000 now U.S. Pat. No. 6,265,718, which is acontinuation of U.S. application Ser. No. 09/208,733, filed Dec. 9,1998, now U.S. Pat. No. 6,057,547, which is a continuation of U.S.application Ser. No. 08/831,153, filed Apr. 1, 1997, now U.S. Pat. No.5,939,719, which is a continuation of U.S. application Ser. No.08/710,239, filed Sep. 13, 1996, now U.S. Pat. No. 5,714,756, which is adivisional of U.S. application Ser. No. 08/428,358, filed Apr. 21, 1995,now U.S. Pat. No. 5,877,891, which is a divisional of U.S. applicationSer. No. 07/850,677, filed Mar. 13, 1992, now U.S. Pat. No. 5,448,399,and U.S. application Ser. No. 07/850,669, filed Mar. 13, 1992, now U.S.Pat. No. 5,376,790, each of which is incorporated herein by reference inits entirety.

FIELD OF THE INVENTION

This invention relates to scanning probe microscopes, which are used toobtain extremely detailed analyses of the topography and othercharacteristics of samples such as semiconductor devices and datastorage media and, more particularly, to scanning probe microscopeswhich are classified as scanning force microscopes or scanning tunnelingmicroscopes.

BACKGROUND OF THE INVENTION DEFINITIONS

“Scanning probe microscope” (SPM) means an instrument which provides amicroscopic analysis of the topographical features or othercharacteristics of a surface by causing a probe to scan the surface. Itrefers to a class of instruments which employ a technique of mapping thespatial distribution of a surface property, by localizing the influenceof the property to a small probe. The probe moves relative to the sampleand measures the change in the property or follows constant contours ofthe property. Depending on the type of SPM, the probe either contacts orrides slightly (up to a few hundred Angstroms) above the surface to beanalyzed. Scanning probe microscopes include devices such as scanningforce microscopes (STMs), scanning tunneling microscopes (STMS),scanning acoustic microscopes, scanning capacitance microscopes,magnetic force microscopes, scanning thermal microscopes, scanningoptical microscopes, and scanning ion-conductive microscopes.

“Probe” means the element of an SPM which rides on or over the surfaceof the sample and acts as the sensing point for surface interactions. Inan SFM the probe includes a flexible cantilever and a microscopic tipwhich projects from an end of the cantilever. In an STM the probeincludes a sharp metallic tip which is capable of sustaining a tunnelingcurrent with the surface of the sample. This current can be measured andmaintained by means of sensitive actuators and amplifying electronics.In a combined SFM/STM the probe includes a cantilever and tip which areconductive, and the cantilever deflection and the tunneling current aremeasured simultaneously.

“Cantilever” means the portion of the probe of an SFM which deflectsslightly in response to forces acting on the tip, allowing a deflectionsensor to generate an error signal as the probe scans the surface of thesample.

“Tip” in an SFM means the microscopic projection from one end of thecantilever which rides an or slightly above the surface of the sample.In an STM, “tip” refers to the metallic tip.

“Package” means an assembly which includes the cantilever and tip, achip from which the cantilever projects, and may include a plate onwhich the chip is mounted.

“Scanning Force Microscope” SFM (sometimes referred to as Atomic ForceMicroscope) means an SPM which senses the topography of a surface bydetecting the deflection of a cantilever as the sample is scanned. AnSFM may operate in a contacting mode, in which the tip of the probe isin contact with the sample surface, or a non-contacting made, in whichthe tip is maintained at a spacing of about 50 Å or greater above thesample surface. The cantilever deflects in response to electrostatic,magnetic, van der Waals or other forces between the tip and surface. Inthese cases, the deflection of the cantilever from which the tipprojects is measured.

“Scanning Tunneling Microscope” (STM) means an SPM in which a tunnelingcurrent flows between the probe and the sample surface, from which it isseparated by approximately 1-10 Å. The magnitude of the tunnelingcurrent is highly sensitive to changes in the spacing between the probeand sample. STMs are normally operated in a constant current mode,wherein changes in the tunneling current are detected as an errorsignal. A feedback loop uses this signal to send a correction signal toa transducer element to adjust the spacing between the probe and sampleand thereby maintain a constant tunneling current. An STM may also beoperated in a constant height mode, wherein the probe is maintained at aconstant height so that the probe-sample gap is not controlled, andvariations in the tunneling current are detected.

“Kinematic mounting” means a technique of removably mounting a rigidobject relative to another rigid object so as to yield a very accurate,reproducible positioning of the objects with respect to each other. Theposition of the first object is defined by six points of contact an thesecond. These six points must not over or under constrain the positionof the first object. In one common form of kinematic mounting, threeballs on the first object contact a conical depression, a slot (orgroove) and a flat contact zone, respectively, on the second object.Alternatively, the three balls fit snugly within three slots formed at120° angles to one another on the second object. The foregoing are onlyexamples; numerous other kinematic mounting arrangements are possible.According to the principles of kinematic mounting, which are well knownin the mechanical arts, six points of contact between the two objectsare required to establish a kinematic mounting arrangement. For example,in the first illustration given above, the first ball makes contact atthree points on the conical surface (because of inherent surfaceimperfections, a continuous contact around the cone will not occur), twopoints in the slot, and one point on the flat surface, giving it a totalof six contact points. In the second illustration, each ball contactspoints on either side of the slot into which it fits.

THE PRIOR ART

Scanning probe microscopes (SPMs) are used to obtain extremely detailedanalyses of the topographical or other features of a surface, withsensitivities extending down to the scale of individual atoms andmolecules. Several components are common to practically all scanningprobe microscopes. The essential component of the microscope is a tinyprobe positioned in very close proximity to a sample surface andproviding a measurement of its topography or some other physicalparameter, with a resolution that is determined primarily by the shapeof the tip and its proximity to the surface. In a scanning forcemicroscope (SFM), the probe includes a tip which projects from the endof a cantilever. Typically, the tip is very sharp to achieve maximumlateral resolution by confining the force interaction to the end of thetip. A deflection sensor detects the deflection of the cantilever andgenerates a deflection signal, which is then compared with a desired orreference deflection signal. The reference signal is then subtractedfrom the deflection signal to obtain an error signal, which is deliveredto a controller. There are several types of deflection sensors. One typeuses an optical interferometer as described in an article by D. Rugar etal., Review of Scientific Instruments, Vol. 59, p. 2337 (1988). Mostcommercial SFMs, however, employ a laser beam which is reflected fromthe back of the cantilever and use a photodetector to sense the angularmovement of the beam as the cantilever is deflected. The probe(cantilever and tip) and deflection sensor are normally housed in a unitreferred to as a head, which also contains circuitry for preamplifyingthe signals generated by the deflection sensor before they are passed toa controller. An image is formed by scanning the sample with respect tothe probe in a raster pattern, recording data at successive points inthe scan, and displaying the data on a video display. The development ofscanning (or atomic) force microscopy is described in articles by G.Binnig et al., Europhys. Lett., Vol. 3, p. 1281 (1987), and T. R.Albrecht et al., J. Vac. Sci. Technology, A6, p. 271 (1988). Thedevelopment of the cantilever for SFMs is described in an article by T.R. Albrecht et al., entitled “Microfabricated Cantilever stylus forAtomic Force Microscopy”. J.Vac. Sci. Technol., A8, p. 3386 (1990).Other types of SPMs, such as scanning capacitance or scanning magneticforce microscopes, also use similar deflection sensors.

A scanning tunneling microscope (STM) is similar to an SFM in overallstructure, but the probe consists of a sharpened conductive needle-liketip rather than a cantilever. The surface to be mapped must generally beconductive or semiconductive. The metallic needle is typicallypositioned a few Angstroms above the surface. When a bias voltage isapplied between the tip and the sample, a tunneling current flowsbetween the tip and the surface. The tunneling current is exponentiallysensitive to the spacing between the tip and the surface and thusprovides a representation of the spacing. The variations in thetunneling current in an STM are therefore analogous to the deflection ofthe cantilever in an SFM. The head contains circuitry for biasing thetip with respect to the sample and preamplifying the tunneling currentbefore it is passed to a controller.

Before a desired region on the sample can be analyzed in an SFM, it mustbe positioned properly with respect to the probe, that is, the probemust be positioned above the location on the sample to be examined andmust be brought into contact or close proximity with the sample. Thisrequires two types of movement: first a lateral (x, y) movement and thena vertical (z) movement. The translations required to do this are beyondthe limited range of the x, y, z fine movement stage. This process maybe accomplished manually or with “coarse” positioning stages. In thelatter case, the sample or head is mounted on a coarse x, y stage, whichis capable of horizontal movement in any direction to properly positionthe sample beneath the probe. Typically, a coarse x, y stage has atranslation range of around 25 mm.

A coarse z stage is used to position the probe vertically with respectto the sample. It is desirable that a z coarse stage permit maximumsample-probe separation (e.g., 30 mm or more if possible). In thisposition, the probe can be changed if necessary and/or a differentsample may be placed in the SPM. The coarse z stage is also adjustableto bring the probe to a distance (e.g., of around 100 μm) where theposition relationship between the probe and sample can be viewed throughan accessory optical microscope. The coarse x, y stage is then used tomove the sample horizontally with respect to the probe until the opticalmicroscopic view indicates that the probe is positioned over a featureor area of the sample which is to be analyzed. The coarse z stage isthen adjusted carefully so as to bring the probe to the sample graduallyuntil the scanner fine x, y, z stage (scanner, described below) and itsassociated feedback loop (described below) take over to maintain aproper probe-sample separation. The final approach requires a resolutionof about one micron and must be performed delicately to avoid crashingthe probe into the sample.

In all of the coarse and fine (scanning) movements, the key factor isthe position and movement of the probe relative to the sample. Theactual movement may be performed by the probe or the sample or both.

The scanning operation is performed by a fine x, y, z stage, or scanner,which has a range of about 1-300 μm in the x and y directions and about1-15 μm in the z direction. The scanner typically moves the samplehorizontally such that the probe follows a raster-type path over thesurface to be analyzed. In the fast scan direction, a computer collectsa line of data at a series of points. Movement in the slow scandirection positions the scanner for the next line of data points to betaken. The resulting image will be made up of individual pixels.Usually, all data are collected in the same fast scan direction, thatis, data are not collected along the reverse path.

In most SPMs, the scanning movement is generated with avertically-oriented piezoelectric tube. The base of the tube is fixed,while the other end, which may be connected to either the probe or thesample, is free to move laterally as an input voltage signal is appliedto the piezoelectric tube. The use of a piezoelectric tube in thisapplication is well known and is described, for example, in an articleby Binnig and Smith, Review of Scientific Instruments, Vol. 57, pp. 1688(August 1986).

Fine movement in the z direction is normally also obtained using apiezoelectric device. FIG. 11A illustrates the prior art feedback loopfor controlling the movement of the scanner in the z direction. Assumingthe device is an SFM or other device that uses a similar type ofcantilever, a deflection sensor measures the deflection of the probe andgenerates an error signal E which is the difference between thedeflection signal and a reference signal. The error signal E is passedto a controller which applies a z feedback voltage signal Z_(v) whichdrives a scanner in the z direction so as to maintain a constantcantilever deflection as the sample is scanned horizontally. Forexample, if the probe encounters a bump in the sample surface, thefeedback signal Z_(v) will cause the scanner to increase the separationbetween the probe and the sample and thereby maintain a constantcantilever deflection. The feedback signal Z_(y) thus represents thesample topography and can be used to form an image. Alternatively, theSFM nay be operated with the x feedback adjusted so as to compensateonly for large topographical features such as sample slope, and theerror signal E may be used to generate a representation of the samplesurface. This mode has disadvantages. For example, damage to the surfaceor probe may occur f the probe deflection exceeds a maximum limit.

In the prior art the function of the controller may be achieved purelyby analog circuitry, in which the error signal is appropriatelyprocessed in order to optimize the performance of the feedback loop.Alternatively, the error signal may be digitized, and the processing maybe performed digitally using a computer or digital signal processingdevice, such as are commonly known and available. In the latter case,the digital signals are converted back into analog form before they aretransmitted to the scanner.

The feedback loop in an STM operates in a very similar manner, theprimary difference being that the error signal which is sent to thecontroller is generated by the tunneling current rather than thedeflection of a cantilever. The difference of this current from a setvalue, which is a function of the spacing between the probe and thesurface, is used by the controller to determine the z feedback signalwhich it sends to the scanner. The feedback signal adjusts the scannerposition to maintain constant spacing between the probe and the surface.Since the tunneling current depends exponentially on the spacing betweenthe probe and the surface, a high vertical sensitivity is obtained.Because the probe may be atomically sharp, the lateral sensitivity isalso high.

The topography of the sample is often displayed in a format known as agrey scale, in which the image brightness at each pixel point is somefunction of the surface height at that point on the surface. Forexample, when the z feedback signal applied to the scanner causes it tocull the sample back (e.g., to compensate for the height of a peak onthe surface) the corresponding data point on the display is paintedbright. Conversely, when the sample is moved towards the probe (e.g., tocompensate for the depth of a valley) the data point is painted dark.Each pixel on the display thus represents an x, y position on the sampleand the z coordinate is represented by intensity. The z position canalso be represented numerically or graphically with high precision.

As stated above, it is known to measure the deflection of the cantileverin an SFM by directing a laser beam against a smooth surface on the backof the cantilever and detecting changes in the position of the reflectedlaser beam as the cantilever is deflected. The shift in the laser beamposition is normally detected by a bi-cell position-sensitivephotodetector (PSPD). With conventional SFM's, this detection circuitrygenerally obstructs an optical view of the probe positioned over thesample. application Ser. No. 07/668,886, filed Mar. 13, 1991, which isincorporated herein by reference, describes a deflection sensor in whichthe laser beam is reflected from a mirror positioned to a side of thecantilever so that the view from directly above the cantilever is notobstructed. That application also describes a system for kinematicallymounting the mirror in the deflection sensor and a mechanism forkinematically mounting the head on the base.

These represent significant improvements over the prior art. However, anumber of difficulties remain with prior art scanning probe microscopes,including the following:

1. In an SFM, the probe normally wears out and must be replaced afterseveral samples have been scanned. Moreover, It is often desirable tochange probes between samples to avoid contaminating the surface of anew sample with material accumulated on the tip from a previous samplesurface. With the type of deflection sensor described above, the laserbeam Rust be precisely directed to a very small area, on the order of 20microns wide, on the back of the cantilever. Each time the cantilever isreplaced, the laser beam must be readjusted so that it strikes the sameposition. Aligning the deflection sensor is a time-consuming procedureand typically requires a very precise position stage. For example,scanning a sample might take 30 minutes, and repositioning the laserspot might take an additional 15 minutes. Thus, a large portion of thetime spent on a sample must be used to realign the deflection sensorafter the probe has been replaced.

2. Different preamplification circuitry is required to amplify eitherthe signal from the deflection sensor in an SFM or the tunnelingcurrents from the tip in an STM. These preamps must be located in thehead, close to the source of their respective signals, to reduce noisepickup. Likewise, SFMs and STMs typically require different probes, alsolocated in the head. In the prior art arrangements, a head is dedicatedeither to an SFM or to an STM. Consequently, the head must be disengagedand replaced in order to switch between SFM and STM operating modes.This is a time consuming procedure. Moreover, each head is an expensivecomponent.

3. A bi-cell PSPD is typically used in the deflection sensor of an SFMto detect changes in light position caused by cantilever deflection. Thesensitivity of bi-cells to these changes depends nonlinearly on theinitial light position. Sensitivity is greatest when the light strikesthe center of the PSPD, thereby producing a zero initial signal. As thelight position moves off-center (i.e., an initial signal offset ispresent), sensitivity drops. If the initial offset is too large, thebi-cell cannot function, since light strikes only one of the cells. Thisnonlinear position response is further adversely affected by intensityvariations across the width of the light spot. To minimize theseeffects, frequent and time-consuming adjustments to zero the initialsignal offset are necessary before running the microscope and each timea probe is changed.

4. The coarse x, y stage in an SPM is often a stacked structure whichhas at least three levels: a fixed base, a y stage, and an x stage. Thisconfiguration has a relatively large mechanical loop, i.e., thermal andmechanical displacements in these individual stages are cumulative andcan affect the spacing between the probe and sample. These displacementsare a significant source of noise in the data. A configuration with alarge mechanical loop may also be unstable.

5. Piezoelectric scanners inherently exhibit nonlinear behavior whichincludes hysteresis (where the scanner position for a given controlvoltage is a function of past history of movement), creep (where thescanner position gradually drifts in response to an applied voltage),and nonlinear response (where the scanner position is a nonlinearfunction of applied voltage). In addition, bending of a piezoelectrictube scanner is inherently associated with its lateral movement andcauses it to tilt. These nonlinear effects contribute undesirably to thedata image and require some means for scan correction. U.S. Pat. No.5,051,646 describes a method to correct for these nonlinearities byapplying a nonlinear control voltage to the piezoelectric scanner.However, this method is “open loop”, i.e., it does not use feedback andhas no means to determine and correct the actual scanner motion due tothe applied nonlinear input signal. Application Ser. No. 07/766,656,filed Sep. 26, 1991, which is incorporated herein by reference,describes a method of correcting for nonlinearities in the x, y lateralmotion of the scanner that is “closed loop”, i.e., it does use feedback.However, the method does not take into account the bending of apiezoelectric tube scanner, which causes tilt.

6. In typical SPMs the problem of hysteresis requires that each line ofdata in the raster scan be collected in the same direction, since datacollected in the reverse direction includes the effects of hysteresis.As a consequence, each line of the raster scan must be traversedtwice—once to collect data and once to return along the same path (orvice versa). The length of time necessary to generate an image is thussignificantly greater than what it might be without hysteresis effects.Moreover, hysteresis problems prevent the use of data collected in theforward scan of a line to adjust the scan parameters before generatingan image from scanning the line in the reverse direction.

7. Another source of error in the data image arises due to the thicknessof the sample. As a piezoelectric tube scanner bends to thereby producea lateral motion of a sample (or probe) mounted on it, the sample (orprobe) moves in an arc-shaped path. As the thickness (verticaldimension) of the sample increases, a given input signal to thepiezoelectric tube scanner therefore produces a larger horizontaltranslation of the surface of the sample.

8. In order to position the sample relative to the probe, it is usefulto have both a coaxial (on-axis) and oblique view of the same using anoptical microscope. These views provide means to monitor finepositioning of the sample relative to the probe. The coaxial viewassists in positioning the probe over the feature of the sample to bemeasured. The oblique view permits accurate adjustment of probeorientation (for instance, cantilever tilt) relative to the samplesurface. Conventional SPMs provide both these features; however, theyare provided in two separate, annually operated microscopes, which areunwieldy to use. Obtaining these dual views is thus inconvenient.

9. In prior art SPMs the piezoelectric tube scanner cannot We operatedat a rate greater than its resonant frequency. Above its resonantfrequency, the response of the scanner to an input voltage signal isgreatly reduced and out of phase with the input signal.

10. Prior art SPMs do not permit the adjustment of scanning parameterssuch as scanning rate or probe path in response to topographicalfeatures encountered by the probe.

SUMMARY OF THE INVENTION

In the scanning probe microscope of this invention, a package, whichcontains a probe, is kinematically mounted onto a cartridge, which inturn is kinematically mounted in the head. In order to switch probes,the cartridge is removed from the head and a new package, containing anew probe, is mounted onto the cartridge, which is then remounted in thehead. The cartridge and package are thus both easily removed andreplaced. The kinematic mounting techniques used ensure that the probeis positioned in the head within an accuracy of approximately 20microns. This arrangement permits SFM and STM probes, and other types ofprobes, to be easily interchanged. Time-consuming adjustment to positionthe deflection sensor in an SFM is not required after probe replacement,as it is in the prior art.

The SFM probe consists of a flexible cantilever which projects from oneend of a microfabricated chip. The chip is attached to a plate to formthe package. This package also contains precisely aligned kinematicmounting points for securing it to the cartridge. The chip may beattached to the plate using integrated circuit (c) mounting techniques,a gluing process, or other methods. Alternatively, a combined,Integrated plate and chip can be microfabricated, and precisely alignedkinematic mounting points can be formed on it using lithographic means(for instance) to allow the package to be kinematically mounted on thecartridge. A chip or a package containing a chip may also bekinematically mounted directly in the head, thereby omitting thecartridge, or a chip may be kinematically mounted directly on thecartridge.

The deflection sensor of this invention uses a light beam deflectionsensor to detect the angular movement of the light beam that occurs whenthe cantilever deflects. A linear position-sensitive photodetector(PSPD), i.e., an analog PSPD that can provide continuous linearinformation about the position of a light spot on the detector's activesurface, is used to detect this movement instead of a bi-cell PSPD. Alinear PSPD has a highly linear, continuous response to the position ofthe incident light beam and is much more tolerant of an initial offsetin light position. Frequent adjustments of the PSPD to zero the initialoffset are no longer necessary as they are in the prior art. Sinceoccasional adjustments may be necessary to center the light on the PSPDto minimize noise, a position adjustment mechanism for the linear PSPDis provided.

The head of the scanning probe microscope contains circuitry capable ofpreamplifying both SFM and STM signals, thereby eliminating the need fortwo different heads which must be switched when shifting betweenscanning force and scanning tunneling microscopy.

A single, non-stacked coarse x, y stage holds both the sample andscanner. The coarse x, y stage is slidably clamped to the base and isloaded against it at three contact points. It is normally heldstationary by friction between the clamping surfaces and the base. Whenthe position of the coarse x, y stage is adjusted, the three contactpoints slide across a smooth surface on the base, which may preferablybe glass microscope slides. Horizontal translation of the coarse x, ystage is accomplished by two adjustment members which are orientedperpendicularly to one another. In a preferred embodiment, eachadjustment member is a screw which is threaded through a fixed nut anddriven by a stepper motor. An end of one screw is ball-tipped and makesa single point of contact with an edge of the coarse x, y stage. An endof the other screw makes contact with a pushing plate, which in turnmakes two points of contact with another edge of the x, y coarse stage.The pushing plate slides on a rail mounted on the underside of the base.The x, y stage and pushing plate are biased against their respectivecontact points by loading springs. The configuration of six contactpoints which define the position relative to the base of the coarse x, ystage (three clamping points, two pushing plate points, one screw end)constitute a stable kinematic mount. The x and y stepper motors slidealong respective rails as the screws are advanced and withdrawn. Thefixed nuts represent reference points which are positioned so as tominimize the mechanical loop involved in positioning the coarse x, ystage. There are alternative means of kinematically mounting a singlenon-stacked coarse x, y stage to the base so as to minimize themechanical loop of the configuration which will become apparent in whatfollows.

The coarse z stage comprises three adjustment members which are arrangedin a triangular configuration and regulate the separation between thehead and the coarse x, y stage. In a preferred embodiment, eachadjustment member comprises a screw which is oriented vertically andthreaded through a fixed nut in the base of the microscope. Each screwis driven by a stepper motor which slides along a rail as the screw isadvanced or withdrawn. Each screw is ball-tipped, and the head ismounted kinematically on the three screws. This configuration allowsboth the elevation and tilt of the probe with respect to the sample tobe adjusted.

The scanner (also referred to as the fine x, y, z stage) comprises apiezoelectric tube whose base is fixed to the coarse x, y stage andwhose opposite end is free to move in response to an applied voltage. Aquad-cell PSPD is mounted axially at the upper end of the piezoelectrictube and faces a light source (e.g., a light emitting diode (LED))mounted at the base of the tube. As the upper end of the piezoelectrictube moves horizontally, the position of the light striking thequad-cell PSPD shifts. The quad-cell PSPD thus senses the x, y movementof the free end of the piezoelectric tube and thereby of a samplemounted on it. In addition, two bi-cell PSPDs are mounted on the outersurface of the piezoelectric tube such that they face two light sources(for example LEDs). The outputs from these PSPDs are added together toprovide a z position signal which is insensitive to sample tilt (whichoccurs due to bending of the piezoelectric tube as described above). Thesignals from the axially-mounted PSPD and the twin surface-mounted PSPDsare used in closed feedback loops to correct for the nonlinear behaviorof the tube scanner.

Each of the stepper motors in the coarse z stage trips a limit switchwhen it reaches a maximum vertical position. The limit switches arepositioned so that the head is oriented horizontally relative to thebase when all three limit switches are tripped. With all three limitswitches tripped, i.e., with the probe raised to its maximum heightabove the sample, the thickness of the sample can be measured by thencausing the stepper motors to retract the screws until the probe makescontact with the sample and recording the distance traversed.Measurement of the sample height is used to correct for the horizontalscanning error which arises due to the finite sample thickness. As notedabove, this error results from the bending of the piezoelectric tubescanner as its free end, holding the sample, is displaced laterally inresponse to the input voltage. The measurement is used to adjust the x,y sensitivity of the piezoelectric tube scanner, which is expressed as aunit of scanner displacement per unit of applied bias (e.g., μm/volts).Stepper motors are not required; any sufficiently well-calibrated andreproducible motor will suffice.

The sample thickness needs to be compared to that of a calibratingsample of the system (or reference surface). The reference surface isused to generate a value of the tube's lateral sensitivity (μm/V). Thethickness of the calibrating sample (or reference height) is stored asthe distance (or steps of the stepper motor) the z approach screwstravel from the limit switches to the calibration sample or referencesurface. An arbitrary sample's thickness is measured relative to thiscalibration. A change in the sample thickness affects the calibrationvalues of the scanner through a simple formula as described below. Inthis manner the sample thickness is measured and the sensitivity of thescanner is updated.

A combined on-axis optical view and an oblique optical view of thesample positioned relative to the probe are provided. Either of theseoptical paths is selected by positioning a motorized shutter undercomputer control. The dual optical views obtained using a motorizedshutter, mirrors, and lenses and the means of switching between themadvantageously eliminates the need for two separate optical microscopes.Also, the microscope lenses positioned in the two optical paths (whichcan be either objective or achromat, for instance) are moved under motorcontrol to raise or lower the focal plane and thus focus the image undercomputer control.

The system includes a scanning probe microscope (SPM) graphical userinterface which has a simultaneous on-screen optical view and SPM viewfor user reference. These views are also used to locate and defineregions graphically for the next scan. The image from either of the twooptical paths is focused on a conventional CCD camera by a computercontrolled motorized zoom lens. The motorized zoom motor encoder allowsautomatic control of optical image magnification and optical image size.Calibration of the motorized zoom lens assembly permits accuratecorrelation of features in optical and SPM images. This eliminates theneed for eyepieces for the optical microscope by displaying images on avideo screen. Additionally, since the optical system is parfocal, theimage magnification can be varied either by switching objective lenses(mounted on a conventional turret) or adjusting the motorized zoom lensand the image will remain focused.

On-screen views (both optical and SPM) are coupled to sample movementrelative to the probe. Computerized motors (x,y, and z) and/or thescanner automatically position the sample in a scan region chosen bygraphical means. A desired scan region on the sample can be chosen bygraphically highlighting a portion of an optical image or an SPM image.Automatic positioning of the SPM can then be used to successively narrowthe scan width and zoom in on a feature of interest. Thus manualadjustments to position for the next scan are no longer needed as theyaren't the prior art. The system places scan marks in the optical imageto indicate SPM scan location, thereby creating a scan record. Featuresin the optical image and the SPM image can be accurately correlated.

The SPM of this invention uses an optical control process toautomatically and quickly position the probe to within a few microns ofthe sample surface, by presetting the focal plane of the objective lensa few microns below the probe tip and then bringing this focal planeinto coincidence with the sample. The three z stage motors and the motorcoupled to the optical lens assembly are lowered in unison, moving theprobe tip and the focal plane of the objective lens quickly down towardsthe sample, until software determines that the image of the samplesurface is in focus. The z stage then slows down for final approach.This shortens the time required to bring the probe into proximity orcontact with the surface, or to within the range of the fine x, y, zstage (the scanner).

This system also uses an optical control process to determine the tiltof a sample secured to a sample mount by bringing three different pointson the surface into focus successively and determining the slope of thesample surface from this data. The sample slope is used forautomatically adjusting the tilt of the head (and thereby the probe) soas to make it parallel to the sample surface. This tilt information canalso be used to adjust scanning parameters or image display parametersthat will remove this overall slope from images of the surface. Thus,this process can determine sample slope and probe tilt. (This slope canbe due, for instance, to a crooked sample mount.)

Data image buffers in the user interface of the system are used toautomatically transfer data between data acquisition and imageprocessing modes, thus conserving permanent storage space. Buffers aredisplayed on-screen for visual reference and can be brought into anactive window for image processing. The buffers can include datacollected in real-time or data brought in from a database. Porting thebuffered images automatically between the data acquisition and imageprocessing modes gives the user much greater flexibility to analyze datain real-time, to quickly extract quantitative information, and to doimage processing to determine if it will be worth saving permanently.

The user interface of this system provides a fast one-dimensional FFT(Fast Fourier Transform) performed on a live line trace of the data(i.e., a digital oscilloscope). Providing a live one-dimensional FFTallows the user to extract quantitative information without importingthe image to an analysis program. Furthermore, the ability of thecontroller to perform FFT or other analyses on line data in real timeallows the controller to use the results of the analysis to optimize thepresent scanning and feedback parameters of the SPM system. Moregenerally, the system analytically detects undesirable outputs such as amechanical resonance in the scanning data and then changes the scanningparameters (such as speed) so as to avoid exiting the resonance.

In another application of the ability to perform a one-dimensional FFTin real time, the user can display the live line trace and itsone-dimensional FFT, and can also display the logarithm of the errorsignal. The latter is a useful capability in STM, where the signal(tunneling current) depends exponentially on the spacing between the tipand the sample. The user interface can perform the one-dimensional FFTon an arbitrary line of the data image, including an image retrievedfrom a database, using high and low pass filters which are graphicallyapplied to the line using standard graphical user interface featuressuch as cursors. The resultant filtered line is displayed in real time.

The interface of this system also provides a two-dimensional FFT andapplies high and low pass filters to a reduced region of the sample forincreased processing speed before applying the FFT to the entire dataimage. The use of, for instance, cursors to adjust filtering parametersand the display in real time of the calculation result makes using thevariable and pass filter very intuitive and easy.

The interface of this system also facilitates optimization of parametersfor 3-dimensional rendering of the data image. This rendering is themanner of displaying 3-dimensional data in the form that gives theillusion of depth, slope, shading, etc. on a computer screen. It uses agraphic to show the effect in real time of varying parameters for3-dimensional rendering. Optimized parameters are then applied to thedata image. This significantly shortens the iteration process requiredto achieve optimal 3-dimensional rendering. Any graphic can be used forthis purpose, such as an artificial structure having simple geometriesor a reduced data set such as data from some fraction of the image datato be processed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a general schematic view of an SFM in accordance witha preferred embodiment of the invention.

FIG. 2A illustrates a perspective view of a cantilever chip package anda cartridge to be mounted in an SFM. FIG. 2B illustrates akinematically-mounted chip.

FIG. 3 illustrates a perspective view showing how the cartridge ismounted in the head.

FIG. 4A illustrates a perspective view of the head, showing inparticular the deflection sensor.

FIG. 4B illustrates a perspective view of the mounting mechanism for thelaser alignment mirror in the deflection sensor.

FIGS. 5A and 5B illustrate cartridges for an STM and a combined SFM/STM,respectively.

FIGS. 6A, 6B and 6C illustrate top, side and bottom views, respectively,of the x, y and the z coarse movement stages. FIG. 6D illustrates abottom view of an alternative embodiment of an x, y coarse stage.

FIGS. 7A and 7B illustrate perspective and top views, respectively, of apiezoelectric tube scanner. FIG. 7C illustrates schematically thedeformation of the piezoelectric tube scanner upon the application of aninput voltage. FIG. 7D illustrates a graph showing the hysteresisassociated with a piezoelectric tube scanner.

FIG. 8A illustrates an exploded view of the scanner and x, y and zposition detectors. FIG. 8B illustrates a detailed perspective view ofthe z position detectors.

FIG. 9 illustrates in exaggerated fashion the lateral movement of apiezoelectric tube scanner.

FIG. 10A illustrates a diagram of a circuit for obtaining an outputsignal from each of the z position detectors. FIG. 10B illustrates howthe z position signal is obtained from both z position detectors. FIG.10C illustrates a diagram of a circuit for obtaining x and y positionsignals from the x, y position detector.

FIG. 11A illustrates a conventional feedback loop and data path for anSPM. FIG. 11B illustrates an improved feedback loop in accordance withthe invention. FIG. 11C illustrates an embodiment with the outputdelivered from the z detector. FIG. 11D illustrates an embodiment withthe output of the z position detector delivered to the z controller.FIG. 11E illustrates an embodiment with the output of the z positiondetector delivered to the x, y controller. FIG. 11F illustrates anembodiment with the output of an x, y position detector delivered to thex, y controller.

FIG. 12 illustrates the two optical paths.

FIG. 13 illustrates the data acquisition user interface.

FIG. 14 illustrates the stage motor control process.

FIG. 15 illustrates the positioning of the optical focal plane below theprobe.

FIGS. 16-18 illustrate the data analysis user interface.

DESCRIPTION OF THE INVENTION

A general schematic view of a scanning force microscope (SFM) 100 inaccordance with the invention is shown in FIG. 1. A cantilever 102 fromwhich a tip 101 projects is positioned over a sample 104. A deflectionsensor 106, located in a head 108, detects the deflection of cantilever102 as it scans the surface of sample 104, and sends an error signal toa controller 110. Cantilever 102 and tip 101, also referred to herein asa probe, are also located in the head. Cantilever 102 approaches sample104 by means of a z coarse stage 112, which links head 108 to a base114. Situated on base 114 is an x, y coarse stage 116 which positionsthe sample horizontally at the proper position below cantilever 102. Ascanner (x, y, z fine stage) 118 is mounted in x, y coarse stage 116 andsupports sample 104. Controller 110 generates an x, y scan signal whichactuates scanner 118 to move sample 104 in a specified scanning patternunder cantilever 102. Controller 110 also uses the error signal providedby deflection sensor 106 to generate a z feedback signal which causesscanner 118 to alter the vertical position of sample 104 so as tomaintain a constant deflection of cantilever 102. This z feedback signalis the output of scanning force microscope 100 and may be used togenerate an SPM image 120. Alternatively, the image may be generated byusing the error signal from deflection sensor 106. Other ways ofgenerating an image in accordance with an aspect of this invention aredescribed below.

In scanning force microscope 100, z coarse stage 112 and x, y coarsestage 116 are used to position cantilever 102 above a selected portionof sample 104. Scanner 118 provides the scanning function and maintainsa selected deflection of cantilever 102 during a scanning cycle. Thus, zcoarse stage 112 has a vertical range of approximately 25 mm, and x, ycoarse stage 116 has a horizontal range of approximately 25 mm, whilescanner 118 has horizontal and vertical translation ranges of around 100μm and around 10 μm, respectively.

An optical view 122 of both the cantilever 102 and a portion of sample104 is provided by an optical viewing assembly 124, which includes anobjective lens 126. Optical viewing assembly 124 provides combinedcoaxial and oblique angle magnified views of cantilever 102 and sample104.

The various components and modes of operation including the userinterface of SFM 100 will now be described in greater detail, startingwith a mechanism for mounting cantilever 102 in head 108, and continuingwith the structures of deflection sensor 106, z coarse stage 112, x, ycoarse stage 116, scanner 118 and optical viewing assembly 124.

Head Structure

As shown in FIG. 2A, which is a bottom view, cantilever 102 projectsoutward From one end of a chip 202, which may be microfabricated fromsilicon. Chip 202 is secured to an alumina plate 204 using glue andstandard IC mounting techniques or other alignment methods.Alternatively, the plate may be made of some other material. Chip 202and plate 204 together constitute a package 200. Plate 204 has threerectangular slots 206, 208 and 210 which are precisely laser-machined inalumina plate 204 and are oriented at an angle of 120° to each other.Slots 206, 208 and 210 form kinematic mounting points for package 200,and they fit accurately over balls 212, 214 and 216 which are attachedto a U-shaped cantilever cartridge 218. A spring clip 220 ensures thatpackage 200 is held securely against cantilever cartridge 218, withballs 212, 214 and 216 positioned in slots 206, 208 and 210,respectively. Spring clip 220 also allows package 200 to be removed andreplaced easily from cantilever cartridge 218.

Formed in cantilever cartridge 218 are a cone 222, a lot 224 and a flat226 which serve as kinematic contacts for mounting it in head 108. Cone222 and slot 224 are located on the respective arms of U-shapedcantilever cartridge 218 while flat 226 is located near the middlesection of cantilever cartridge 218. As illustrated in FIG. 3, cone 222,slot 224 and flat 226 are positioned o that they coincide with threeballs 300, 302 and 304 in head 108. Ball 300 fits in cone 222, ball 302fits in slot 224, and ball 304 contacts flat 226, thereby providing akinematic mount between cantilever cartridge 218 and head 108. Springclips 306 hold cartridge 218 securely in place in head 108. As mentionedearlier, various other kinematic mounting techniques may also be usedfor mounting package 200 on cartridge 218 and for mounting cartridge 218in head 108.

Alternatively, kinematic mounting means may be used to mount aprobe-containing package directly in the head, thereby omitting theremovable cartridge. Moreover, as shown in FIG. 2B, kinematic alignmenttrenches can be machined or lithographically formed in the chip itself.Such a structure is illustrated in FIG. 28, which shows a chip 244having trenches 240 and 242 formed in it which fit over balls 246, 248and 250. Balls 246, 248 and 250 may be formed in a cartridge or in thehead itself. When balls 246, 248 and 250 are fitted into trenches 240and 242, a kinematic mount is formed. Other types of kinematic mountsmay also be used.

FIG. 4A illustrates a perspective view of head 108 showing thepositioning of cantilever cartridge 218 with respect to deflectionsensor 106. A laser diode 400 produces a focused laser team 402 having afocus diameter or spot size of approximately 25 μm which is directedtowards an alignment mirror 404 from which it is reflected to a selectedarea on the back of cantilever 102. Laser beam 402 is then reflected offthe back of cantilever 102 and strikes a linear position-sensitivephotodetector (PSPD) 406. PSPD 406 may be adjusted with respect to laserbeam 402 by means of an adjustment screw 418. The output of PSPD 406 issent to a preamplifier 420, which amplifies the signal and sends it tocontroller 110 (FIG. 1).

FIG. 4B illustrates an expanded view of the kinematic mounting ofalignment mirror 404 in head 108. Alignment mirror 404 is positioned atthe center of a sphere 408, with a portion of sphere 408 being cut awayto allow laser beam 402 to be reflected from mirror 404 (see FIG. 4A).The top surface of sphere 408 engages a circular hole 422 in a mirrorbracket 424, which is attached to head 108. Mirror adjustment screws 410and 412 are threaded in tapped holes in head 108, and the ends of screws410 and 412 contact a slot 414 and a flat 416, respectively, that areformed in an adjustment member 426 which extends from sphere 408.Springs 428 bias sphere 408 against hole 422, and the tips of screws 410and 412 against slot 414 and flat 416, respectively. Alignment mirror404 is thus kinematically mounted in head 108, and the angularorientation of mirror 404 can be adjusted by turning screws 410 and 412.

This is a variation of an arrangement for mounting an alignment mirrorkinematically in a head as described in application Ser. No. 07/668,886,filed Mar. 13, 1991. The arrangement of components of the deflectionsensor has here been altered to permit closer approach of objectivelens.

Referring again to FIG. 2, slots 206, 208 and 210 allow package 200 tobe positioned on cantilever cartridge 218 to an accuracy of one micron;similarly, cone 222, slot 224 and flat 226 allow cantilever cartridge218 to be positioned in head 108 to an accuracy of one micron. The ICtechniques used to mount chip 202 on plate 204 assure an accuracy ofapproximately 20 microns or better. Accordingly, cantilever cartridge218 can be removed from head 108, and package 200 can be replaced andcantilever cartridge 218 reinstalled in head 108 with an assurance thatthe new cantilever will be positioned to within approximately 20 micronsof the position of the replaced cantilever. Of the same package isreplaced, this margin of error is reduced to about two microns. Sincelaser beam 402 must strike an area about 20 microns wide at the end ofcantilever 102, this method of replacing cantilevers minimizes the needfor adjustments to alignment mirror 404 or PSPD 406 when the cantileveris replaced between scanning operations. The laser beam realignmentprocess with conventional scanning force microscopes, typically requiredeach time a probe is replaced, is time-consuming. As noted above, themounting arrangement of this invention can result in a savings of asmuch as one-third of the time necessary to perform a series of scans.

FIGS. 5A and 5B illustrate, respectively, a cartridge 500 for an STMprobe and a cartridge 502 for a combined SFM/STM probe. Cartridges 500and 502 are mounted in head 108 using kinematic mounts similar to thosein cantilever cartridge 218. STM probe cartridge 500 contains a cone504, a slot 506 and a flat 508. SFM/STM probe cartridge 502 contains acone 510, a slot 512 and a flat 514. These elements function in exactlythe same way as cone 222, slot 224 and flat 226 in cantilever cartridge218. Cartridge 500 holds an STM package 516, which includes a metallictip 518. Since STM package 516 provides a signal representative of thetunneling current at metallic tip 518, a conductive path 520 is providedfor connecting STM package 516 to preamplifier 406. (The position ofconductive path 520 in head 108 is illustrated in FIG. 4A.)

Cartridge 502 holds an SFM/STM package 522, from which a conductivecantilever 524 projects. A conductive path 526 for delivering the STMsignal to preamplifier 406 is also provided. It will be understood thatthe output signal from STM package 516 is directed through conductivepath 520, and no laser beam or PSPD are required. In the case ofcombined SFM/STM package 522, however, output signals flow both throughconductive path 526 and from a PSPD (not shown in FIG. 5B) to providesimultaneous SFM and STM readings. Thus, one can use SFM/STM package 522to measure cantilever deflection while simultaneously monitoring thetunneling current from the conductive cantilever 524.

Conductive path 520 comprises a lead wire 521 which electricallyconnects the conductive tip to a conductive pad 525 on the cartridge. Aspring clip 523 in the head makes electrical contact with pad 525. Thespring clip itself is electrically connected to preamplifier 420.Conductive path 526 comprises a spring-loaded lead wire 527 which isbonded to a conductive pad 528 on the cartridge. A spring clip 529 inthe head makes electrical contact with pad 528. Since the SFM/STMpackage 522 must be removable from the head, spring-loaded lead wire 527rests lightly on a pad 530 on SFM/STM package 522. Spring clips 523 and529 rest lightly on pads 525 and 528, respectively, allowing removal ofthe cartridges. The force applied by spring clips 523 and 529 andspring-loaded lead wire 527 must be very small so as not to disturb thekinematic mounting arrangements. Alternative electrical connectors (suchas plugs) may be used provided that they likewise do not disturb thekinematic mounts.

Referring again to FIG. 4A, preamplifier 420 is located in closeproximity to cantilever 102 (or to any other probe that may be installedin its place) to prevent spurious noise from being picked up andamplified. Preamplifier 420 contains the electronic circuitry necessaryto preamplify both scanning force signals and scanning tunnelingsignals, and therefore can amplify the signal from cantilever cartridge218, from STM probe cartridge 500, or from SFM/STM probe cartridge 502,whichever one of those cartridges is kinematically mounted in head 108.

The arrangement of this invention thus allows a convenient shift fromscanning force microscopy to scanning tunneling microscopy (or combinedSFM/STM), by simply replacing an SFM probe cartridge with an STM probe(or SFM/STM probe) cartridge. Thus it is not necessary to use separateSFM and STM heads, as in conventional scanning probe microscopes. Asingle head is used to perform both scanning force and scanningtunneling microscopy, thereby significantly reducing the time necessaryto switch between SFM and STM, and reducing the expense of thiscapability.

Coarse Sample Movement Stages

FIGS. 6A, 6B and 6C illustrate schematically top, side and bottom viewsof x, y coarse stage 116 and z coarse stage 112. Axes are marked on thediagrams for clarity. As shown in FIG. 6B, x, y coarse stage 116 ispositioned in an aperture 602 in base 114. Coarse stage 116 is asandwich-like structure consisting of a top plate 604 and a bottom plate606 which are bolted together via a metal piece 607 which fits inaperture 602. The entire top plate 604 is visible in FIG. 6A and theentire bottom plate 606 is visible in FIG. 6C. Scanner 118 is insertedinto an opening in x, y coarse stage 116, and is attached only to topplate 604 to permit easy removal. Metal piece 607 has edges 610 whichare separated sufficiently from edges 608 of aperture 602 to permit x, ycoarse stage 116 to move throughout the required range. (The range of x,y coarse stage 116 in the y direction is somewhat greater than in the xdirection so that it can be pushed from under head 108 to allow thesample to be changed easily.) FIGS. 6A and 6C show edges 608 and inneredges 610 as hatched lines.

Top plate 604 rests on base 114 via three balls 612 which are attachedto top plate 604, and a clamping effect is obtained by threespring-loaded-balls 614 which are attached to bottom plate 606 atpositions opposite balls 612. As shown in FIGS. 6A and 6C (hatchedlines) balls 612 and spring-loaded balls 614 are positioned in atriangular arrangement. To permit x, y coarse stage 116 to slidesmoothly on base 114, balls 612 and 614 contact glass pieces 616, whichare attached to the upper and lower surfaces of base 114 as shown inFIG. 6B. Glass pieces 616 are preferably ordinary glass microscopeslides, and balls 612 and 614 are preferably made of brass. Thiscombination allows x, y coarse stage 116 to slide smoothly with respectto base 114.

FIG. 6C shows x, y coarse stage 116 viewed from the bottom of base 114.The locations of edges 608 of aperture 602 and spring-loaded balls 614and scanner 118 are shown as hatched lines. Also shown are twohorizontal stepper motor assemblies 618 and 620 and a y pushing plate652. Pushing plate 652 is attached to the bottom of base 114 by twoslide mechanisms 653, which permit it to move in the y direction. Twoballs 655 are fixed to an edge of pushing plate 652 and springs 657 biasballs 655 against a smooth straight edge 659 of bottom 606.

Stepper motor assembly 618 which moves the stage in the x direction asindicated includes a stepper motor 622, the drive shaft of which isaxially connected via a flexible coupler 624 to a screw 626 which isthreaded through a fixed nut 628 mounted on base 114. Stepper motor 622slides on a slide rail 630 mounted on base 119 as screw 626 advances orretreats through fixed nut 628. A pair of springs 632 bias an edge 634of bottom plate 606 against a ball tip 636 of screw 626. Limit switches627 limit the travel of stepper motor 622 on slide rail 630. Steppermotor assembly 618 is also shown in FIG. 6B.

Similarly, stepper motor assembly 620 which moves the stage in the ydirection as indicated includes a stepper motor 638 the drive shaft ofwhich is axially connected via a flexible coupler 640 to a screw 642which is threaded through a fixed nut 644 mounted on base 114. Steppermotor 638 slides on slide rail 646 mounted on base 114 as screw 642advances or retreats through fixed nut 644. A pair of springs 648 bias asmooth straight edge 650 of y pushing plate 652 against a ball tip 654of screw 642. Limit switches 643 limit the travel of stepper motor 638on slide rail 646.

The operation of x, y coarse stage 116 can now be described. When x, ycoarse stage 16 is at rest, it is supported by balls 612 which arepressed against glass pieces 616 by gravity and by spring loaded balls614. When movement in the x direction is desired, stepper motor 622 isturned on, turning screw 626 in fixed nut 628. If screw 626 is rotatedclockwise, it advances through fixed nut 628, pressing ball tip 636against edge 634 and pushing bottom plate 606 to the left (in FIG. 6C).If screw 626 is rotated counterclockwise, its tip retracts from edge634, and springs 632 contract, pulling bottom plate 606 to the right. Ineither case, balls 655 slide along edge 659 of bottom plate 606. Ypushing plate 652 is prevented from moving in the x direction by slidemechanisms 653. When movement in the y direction is desired, steppermotor 638 is turned on, turning screw 642 in fixed nut 644. If screw 642is rotated clockwise it advances through fixed nut 644, pressing balltip 654 against edge 650 of y pushing plate 652. Y pushing plate 652slides in the y direction (downward in FIG. 6C), guided by slidemechanisms 653. Since springs 657 bias edge 659 of bottom plate 606against balls 655, bottom plate 606 is also pulled in the y direction(downward in FIG. 6C). This process is reversed when screw 642 isretracted. Springs 648 pull y pushing plate against ball tip 654, and ypushing plate slides in the reverse direction (upward in FIG. 6C). Balls655 press on edge 659, pushing bottom plate 606 upward. Edge 634 slidesagainst ball tip 636.

The position of x, y coarse stage 116 is thus defined—kinematically—bysix contact points: the three contact points between balls 612 and glasspieces 616, the two contact points between balls 655 and bottom plate606, and the contact between ball tip 636 of screw 626 and bottom plate606. This assures that there is only one unique position of x, y coarsestage 116 for each setting of screws 626 and 642.

This design significantly reduces the effect that dimensional changesand vibrations can have on the position of the sample relative to theprobe. This is an important consideration in an SPM, since dimensionalor other changes on the order of a micron or less can significantlydegrade the quality of the image. Since stepper motors 622 and 638 aremounted on slide rails and flexibly coupled to screws 626 and 642,respectively, which in turn are driven through fixed nuts 628 and 644,the effect of thermal expansion or vibration between a motor and a fixednut will be to move the motor along its slide rail. Only displacementsthat occur on the other side of fixed nuts 628 and 644 can affect theposition of the sample relative to the probe. By this configurationusing “floating” motors and a single, non-stacked x, y stage, themechanical loop of the coarse translation stage is significantlyreduced, especially when compared with stacked x, y stageconfigurations. This minimizes the effect of mechanical and thermalvariations on the spacing between the probe and the sample.

There are numerous alternative embodiments of this design. For example,the position of the y stepper motor can be reversed so that it pushes inthe opposite direction against the y pushing plate (upwards in FIG. 6C).The disadvantage of this arrangement, however, is that any dimensionalchanges or vibration in the y pushing plate will be transferred to thex, y coarse stage.

Another alternative embodiment is illustrated in FIG. 6D. Elements inFIG. 6D that are identical to those shown in FIG. 6C are similarlynumbered. In this embodiment, an extended y pushing plate 661 is used,and stepper motor 622 is mounted on the y pushing plate 661 as shown(instead of the base). An extended screw 667 is coupled to the driveshaft of stepper motor 622 and journaled in a fixed bearing 669 which isalso fixed to the y pushing plate 661 as shown. A lead screw 671 havinga ball-tipped contact, pushes against edge 634 of bottom plate 606. Noslide rail is used in this configuration. An extended screw 663 iscoupled to the drive shaft of stepper motor 638 and journaled in a fixedbearing 665. The end of screw 663 is threaded into a tapped hole in ypushing plate 661. Movement of y pushing plate 661 on the y axis isobtained as stepper motor 638 turns screw 663 in the tapped hole in ypushing plate 661. Movement on the x axis is obtained as stepper motor622 turns screw 667 in lead screw 671 so as to push the ball tip of thelead screw against or retract it from bottom plate 606. Otherwise, theoperation is essentially the same as that described in connection withFIG. 6C. Stepper motors 622 and 638 need not be mounted on slides inthis embodiment, but may be if so desired. This embodiment is believedto be equivalent to the embodiment shown in FIG. 6C, having anequivalent mechanical loop, but the machining costs may be somewhathigher.

Numerous other embodiments will be apparent to those skilled in the art.For example, any encoded or well-calibrated motor may be used in placeof stepper motors. The y pushing plate and x, y coarse stage may bebiased against the various contact points by magnets or other biasingmeans besides springs. Smooth surfaces other than glass or brass may beused to support x, y coarse stage 116. A wide variety of arrangementsmay be substituted for the opposing ball-straight edge combination shownin FIGS. 6C and 6D. For example, opposing straight edges and varioustypes of curved surfaces may be used provided that they yield therequisite number of contact points and that a means for assuringcontinuous contact at those points is provided. Two contact points maybe provided with edge 634, and one contact point may be provided withedge 659 of bottom plate 606. The total number of contact points withthose edges must be three.

The z coarse stage 112 is primarily illustrated in FIG. 6B. Threestepper motor assemblies 656 are shown. Stepper motors 658 are mountedvertically on slide rails 660 attached to base 114 and have their driveshafts attached through flexible couplers 672 to z approach screws 664.Z approach screws 664 are threaded through fixed nuts 666 in base 114and have ball tips 668 which contact kinematic mounting points 670 on alower surface of head 108. The relative positions of z approach screws664 are illustrated in FIGS. 6A and 6C, and, as indicated, form atriangular pattern which surrounds bottom plate 606 yet allows it totravel in the x and y directions within the ranges defined by limitswitches 627 and 643. Kinematic contact points 670 on the lower surfaceof head 110 are in this same triangular pattern, and accordingly head108 is stably supported but free to tilt or pitch in any direction asany one or more of z approach screws 664 are adjusted independently.Kinematic contact points 670 may be, for example, a cone, a slot and aflat, respectively. Head 108 is loaded against z approach screws 664 byits own weight and by a biasing spring (not shown). Application Ser. No.07/668,886, filed Mar. 13, 1991, describes a general kinematic mountingarrangement of this kind.

When stepper motors 658 are actuated, individually or in anycombination, they turn z approach screws 664 through fixed nuts 666 andraise or lower ball tips 668. At the same time, stepper motors 658 slidealong slide rails 660. Limit switches 674 and 676 are provided at theupper and lower ends, respectively, of slide rails 660 to turn offstepper motors 658 when they reach preselected upper and lower limits onslide rails 660.

Stepper motors 658 are activated separately by computer controls (notshown). Accordingly, within the ranges defined by limit switches 674 and676, stepper motors 658 can be used to vary the tilt or pitch of head108 and to elevate or lower it to any position above sample 104. Thus,while viewing cantilever 102 through an optical viewing assembly(described below), this motorized arrangement can be actuated so as tocause cantilever 102 to approach the sample surface slowly until thefine movement mechanism takes over and establishes the correctcantilever deflection. Moreover, the tilt and pitch of the cantilevermay be adjusted in order to assure that a corner of the chip does nottouch the sample surface and that the cantilever is pitched properlywith an optimum initial deflection to respond to the profile of thesample surface. Prior art SFMs do not generally have this automatedability, which gives this arrangement flexibility and convenience forpositioning the probe properly with respect to the sample.

Unless stated otherwise, references herein to the z direction refer toaxis that is normal to the sample surface (this is also referred to asthe vertical height). References to the x, y direction refer to axes inthe plane of the sample surface (this is also referred to as thehorizontal direction, lateral direction or scanning direction). Unlessspecifically stated, references to the x, y and z directions do notimply a specific orientation in space (e.g., relative to gravity).

Fine Sample Movement Stage

The structure and operation of scanner 118 are illustrated in FIGS. 7and 8. FIGS. 7A and 7B show a piezoelectric tube scanner 700.Piezoelectric tube scanner 700 is in the form of a hollow cylinder madeof a piezoelectric ceramic material, with four segmented outerelectrodes 702 a, 702 b, 702 c and 702 d on the outer walls and onecontinuous inner electrode 704 covering the cylinder's inner surface. Itis fixed to the base at one end. The application of voltages of oppositesign to opposing outer electrodes (e.g., 702 a and 702 c) drives thefree end of scanner 700 in a lateral direction, as illustrated in FIG.7C, by causing the opposing quadrants of the scanner tube to expand andcontract, respectively. A voltage applied to inner electrode 704 whilethe outside electrodes are held constant causes the scanner 700 toexpand or contract. Since one end of scanner 700 is fixed to x, y coarsestage 116 (see FIG. 6B), this drives its free end, on which the sampleis mounted, in the z direction. Accordingly, depending on the voltageapplied to electrodes 702 a-702 d and 704 the sample moves in the x, yor z directions relative to x, y coarse stage 116 and the probe. Asnoted above, the operation of a piezoelectric tube scanner is describedin an article by G. Binnig et al., Review of Scientific Instruments, v.57, p. 1688 (August 1986).

FIG. 8A illustrates an exploded view showing how scanner 700 is mountedin x, y coarse stage 116. Mounted at the base of scanner 700 is a lightemitting diode (LED) 800, which directs a light beam 802 upward alongthe vertical axis of scanner 700. Another light source may besubstituted for LED 800. A sample platform 805 is mounted at the top ofscanner 700. A quad-cell PSPD 808 is mounted in line with the axis ofscanner 700. Thus, when scanner 700 is in its normal position, lightbeam 802 strikes the center of quad-cell PSPD 808. Attached at rightangles to quad-cell PSPD 808 are bi-cell PSPDs 814 and 816, which extenddownward over the outside surface of scanner 700 and emit light beams822 and 824, respectively. Scanner 700 is enclosed in a housing 815.LEDs 818 and 820 are mounted opposite bi-cell PSPDs 814 and 816,respectively, on housing 815.

FIGS. 8A and 8B show two ways to situate PSPDs 808, 814 and 816 withrespect to the fine stage tube. In FIG. 8A the quad cell PSPD 808 andbi-cell PSPDs 814 and 816 are mounted on a locating fixture 830. Sampleplatform 805 is also mounted on fixture 830. Fixture 830, through somemechanical alignment features, either on fixture 830 or on thepiezoelectric tube 700, is located precisely relative to the tube, toavoid coupling between the detector signals. For example, quad cell PSPD808 must be oriented so that its quadrants are precisely aligned withthe four outer electrodes 702 a-702 d of the tube scanner 700 to ensurethat the detection directions of PSPD 808 will be parallel to the x andy scan directions, respectively. Furthermore, the two bi-cell PSPDs 814and 816 must be oriented so that each senses tilt only about an axisthat is perpendicular to the fast scan direction. This ensures that thesignal from both when added together is insensitive to tilt. Thusfixture 830 aligns properly to the tube 700, and the electronic signalsof the three PSPDs 808, 814, 816 are sent (via wires or flexible printedcircuit board, not shown) to a preamp 813, which is mounted on thescanner housing 815. The preamp 813 should be located near fixture 830to minimize noise pickup.

FIG. 8B shows the fixture 830 replaced by a rigid PCB 804 on which aremounted PSPDs 808, 314 and 816. PCB 804 fits into notches 806 in thetube scanner so as to precisely align PSPDs 808, 814 and 816 with theaxis of tube scanner 700, as well as the scan directions. Electricalconnections are made to quad-cell PSPD 808 and bi-cell PSPDs 814 and 816through conductive lines and vias in PCB 804. PCB 804 may be machined tothe shape shown in FIG. 8B or may be formed of three PCBs joined to oneanother at right angles.

Alternatively, the LEDs may be mounted on scanner 700, and the bi-cellPSPDs may be mounted on an adjacent structure facing the LEDs.

The scanner housing is mounted to the x-y stage 116 by bolting the twotogether.

The position at which the light beam 802 strikes quad-cell PSPD 808provides an accurate indication of the movement of sample platform 805(and hence the sample) in the x and y directions. Similarly, thepositions at which the light beams 822 and 824 strike bi-cell PSPDs 814and 816, respectively, indicate the position of the sample in the zdirection.

FIG. 7D illustrates the movement of the upper end of scanner 700 as afunction of the voltage difference applied to two of the opposingelectrodes 702 a-702 d (e.g., 702 a and 702 c). Two things will be notedabout this behavior. First, the movement of scanner 700 is not a linearfunction of the applied voltage difference, e.g., doubling the voltagedifference results in a position difference which is less than twofold.Second, hysteresis is evident, i.e., the position of scanner 700 for agiven applied voltage depends on whether the voltage is increasing ordecreasing. Third, although not evident from FIG. 7D, scanner 700 alsoexhibits creep, which is a drift in the direction of recent movements.These characteristics lead to distortions in the representation of asurface which must be corrected in order to obtain a true image of thesurface.

FIG. 9 illustrates schematically in an exaggerated fashion twoadditional causes of distortion in the image generated by the scanningprobe microscope. As noted above, the bottom of scanner 700 is fixed tox, y coarse stage 116. As voltages are applied to opposing electrodes,scanner 700 bends, as illustrated in FIG. 9, thereby moving sample 104laterally. This bending has two undesirable effects on the position ofsample 104. First, as sample 104 is moved laterally, it tilts downwardin the direction of its movement. The only position in which sample 104is not tilted is when no voltage differential is applied to the opposingelectrodes of scanner 700. Second, an error is also introduced by thethickness of sample 104. As illustrated in FIG. 9, a point A will appearto be displaced by a horizontal distance h as the thickness of sample104 increases by an amount t.

The outputs of quad-cell PSPD 808 and bi-cell PSPDs 814 and 816 can beused to provide accurate representations of the position of the samplein the x, y and z directions, as described below.

FIG. 10A illustrates the circuit associated with each of the bi-cellPSPDs 814 and 816. Currents from the two cells of each PSPD areconverted into voltages and compared to obtain an output voltage(V_(A)−V_(B)) representative of the position of a light spot on thePSPD. In addition, the voltages are added together and compared with areference voltage. The resulting signal, which is proportional to thetotal intensity of light hitting the PSPD, is connected in a feedbackloop with LED 818 or 820 to drive current to the LEDs in order tocorrect for fluctuations in light intensity.

FIG. 10B shows how the outputs of bi-cell PSPDs 814 and 816 (V_(Z1) andV_(Z2), respectively) are used to obtain a signal V_(topog) whichrepresents changes in sample position excluding the effects of sampletilt. Alternatively, as shown in FIG. 10B, these outputs can be used toobtain a signal V_(tilt) which represents solely a measurement of sampletilt at each point in a scan. For a given tube bending, the output ofone of the bi-cell PSPDs (e.g. V_(Z1)) will represent changes in zposition due to topography plus tilt, since that side of the scannerwill tilt upwards, while the output of the other bi-cell PSPD (V_(Z2))will be due to topography minus tilt, since that side will tiltdownwards. The sum, V_(Z1)+V_(Z2), will therefore represent changes in zdue solely in response to topography. The difference, V_(Z1)−V_(Z2),will give a measure of sample tilt. The outputs from PSPDs 814 and 816are connected electrically to preamp 813 (FIG. 8A). Means are alsoprovided to input the amplified signal to the controller. A connectoralso couples power to the amplifier, LEDs, PSPDs, and scanner tube andcouples the x, y, position signals to their controller (or sectionthereof). A rigid flex is used for these connections, but alternativelywires could be used.

Oppositely mounted PSPDs such as PSPDs 814 and 816 may also be used withnontubular types of piezoelectric scanners to provide a z positionsignal independent of the tilting of the sample.

FIG. 10C illustrates the circuit associated with quad-cell PSPD 808. Aswith bi-cell PSPDs 814 and 816, the outputs of the four cells aresummed, compared with a reference voltage, and fed back to LED 800 tocorrect for intensity variations. In addition, the outputs of cells Aand B are summed and compared with the sum of the outputs of cells C andD to obtain an output V_(y) representing the y position of the sample.The outputs of cells A and C are summed and compared with the sum of theoutputs of cells B and D to obtain an output V_(x) representing theposition of the sample in the x directions.

Several techniques for improving image quality will now be described,many of which utilize the signals representing the actual position ofthe sample in the x, y and z directions.

FIG. 11A illustrates a block diagram of a conventional feedback loop forcontrolling the position of a sample in the z direction. A probe ispositioned relative to a sample, and changes in the probe-to-sampledistance are measured by a deflection sensor. The deflection sensorcompares this signal with a reference signal (for instance, a desireddisplacement value) and generates an error signal E which is passed to acontroller. The controller applies an algorithm to the error signal andgenerates a z feedback voltage Z_(v). The z feedback voltage actuatesthe scanner to bring the probe-to-sample distance back to its desiredlevel (i.e., zero the error signal). The controller may be constructedpurely from analog circuit elements, or from a combination of analog anddigital signal processing elements and software, as is known to personsskilled in the art.

Generally the image is formed by recording the z feedback signal at eachimage point. However, as described above, the scanner typically has anonlinear vertical or horizontal response to an input voltage, and hencethe voltage required to maintain a zero error signal will not be alinear function of sample height. The resulting image will berepresentative of the sample surface topography distorted by thenonlinear response of the scanner. This is a major disadvantage ofconventional SPM systems.

As shown in FIG. 11A, the image may also be generated from the errorsignal E. This may be done in cases where the error signal is nonzerobecause, for example, the controller and scanner are not able to respondfast enough to changes in surface topography to maintain a constantprobe-to-sample distance. If the error signal is sufficiently large, animage generated using the z feedback voltage will not accuratelyrepresent the surface topography, and the prior art solution is to usethe error signal instead. This is not a perfect solution, however,because the error signal itself does not contain all of thetopographical information needed to generate an accurate image.

An improved image may be obtained by using the technique illustrated inFIG. 11B. The error signal is passed through a function generator andadded to the z feedback signal in order to record a composite image. Forsmall values of E, the corrected signal Z_(c) can be assumed to be alinear function of the error signal, i.e., Z_(c)=Z_(v)+αE, where α is aconstant. For larger errors, the corrected signal is some other functionof E, i.e., Z_(c)=Z_(y)+f(E).

FIGS. 11C-11F illustrate feedback loops which have significantadvantages over the prior art feedback loop illustrated in FIG. 11A. InFIG. 11C, a z detector is used to accurately measure the z position ofthe scanner. The z detector may comprise bi-cell PSPDs 814 and 816 (FIG.8A), in which case the output of the z detector is V_(Z1)+V_(Z2) (FIG.10B). As described above, the sum of these two signals excludes theeffects of sample tilt. When the error signal E is successfully zeroed,the output of the z detector provides an accurate image of the surfacetopography, which excludes effects of nonlinear behavior and hysteresisin the scanner. This feedback loop can be combined with other elementswhich add some function of any remaining error to generate a correctedimage (as shown in FIG. 11B).

The feedback loop illustrated in FIG. 11D contains an additionalfeedback path from the z detector to the controller. This improves the zfeedback loop, by permitting feedback parameters such as theproportional gain, integral gain, differential gain, and bandwidth to beadjusted in response to the signal from the z detector. For example, ifthe probe is approaching a very steep surface feature, the response ofthe scanner may be too slow and the probe tip may be damaged. In thiscase, the controller compares the rate of change of Z_(z) with areference signal and delivers a z feedback voltage that causes thescanner to pull the sample away from the probe. (The feature may beindicated by a very bright spot on the image and may be removed usingimage processing software, for example, if it is an isolated feature notof interest.) The feedback loop illustrated in FIG. 11D also permits thescanner to move in the z direction at a rate equal to or faster than itsresonance frequency. If, for example, the topography varies so rapidlythat the scanner must be driven at a frequency at or above its resonancefrequency, a magnified z feedback voltage is applied to compensate forthe inhibited scanner motion. This is equivalent to opening up thebandwidth of the feedback loop.

FIG. 11E shows the controller divided into xy and z sections,respectively, which deliver horizontal and vertical actuating voltagesto the scanner. In this embodiment, the output of the z detector(V_(z1)+V_(z2) in FIG. 10B) is delivered to both the xy and z sectionsof the controller. This configuration allows both the scanning rate andscanning path to be adjusted in accordance with the actual surfacetopography detected by the z detector. For example, if the surfacetopography varies so rapidly that at a given scanning rate that therequired z feedback signal lies outside the bandwidth of the zcontroller, the xy outputs of the controller (X_(v) and Y_(v)) areadjusted to slow the scanning rate. On the other hand, if the probeencounters a very large feature on the surface, the controller mayrecognize a large z gradient (exceeding a reference value) and adjustthe horizontal scan path so that the probe moves around the feature. Thez section of the controller uses the output of the z detector to computea z gradient and if the computed value exceeds a reference value, itinstructs the x, y section to make the necessary adjustments to thescanning path. This process continues so long as the feature isencountered.

In FIG. 11F, the outputs of the x, y detector (V_(x) and V_(y) in FIG.10C) are delivered to the x, y section of the controller. Thisconfiguration provides in addition a correction for the nonlinearitiesinherent in the lateral movement of the scanner, as described inapplication Ser. No. 07/766,656, filed Sep. 26, 1991.

In the embodiments shown in FIGS. 11C-F, if the error signal E isnonzero, it may be passed through a function generator and added to theoutput of the z detector in the manner described in conjunction withFIG. 11B.

We have also discovered several new scanning techniques that may be usedwhen the output of the x, y position detector is fed back to x, ysection of the controller to correct for nonlinearities and hysteresisin the scanner (as shown in FIG. 11F). With the effect of hysteresiseliminated, the position of the scanner for a given x, y input voltageis the same in the forward and reverse scan directions. This means thatdata may be obtained and an image generated in both directions. Thescanner may be stepped to a new line after each scan; there is no needto retrace each line. This reduces the time required to generate animage.

Alternatively, the forward scan on each line may be used to set the scanparameters to optimize values based on the topography of the sample, andthese optimized values can be used when the topography is rescanned inthe reverse direction. For example, if the surface topography varies ata rate greater than the scanner's maximum response rate, the scan ratecan be reduced for that line. Variations in scan parameters such as:scan direction, location and area, dynamic range, feedback filterparameters, tip contact force, tunneling current or voltage, scanningrate, and data processing can all be calculated from the data recordedduring the initial scan and applied during the reverse scan. Othervariations may be appropriate according to the type of piezoelectrictube. Furthermore, such analysis may be used to determine if multiplerepeat scans with different parameters are required to optimally analyzethe surface.

A feedback loop using the x, y position sensor also permits scanning tobe done at a frequency greater than the scanner's resonant frequency inthe x, y direction. With normal prior art devices, the response of thescanner to an input signal above its resonant frequency is greatlyreduced and out of phase. Feedback reflecting the x, y position of thescanner automatically compensates for these effects by adjusting theinput signal.

Similarly, using a feedback loop which includes a z detector (FIG. 11D)permits the scanner to be operated at a frequency, determined by thetopographical fluctuations of the sample, which is greater than theresonant frequency in the z direction.

Optical Viewing Assembly

FIG. 12 shows the optical viewing system for obtaining an optical viewof the probe and sample and also of the deflection sensor positioning.One advantage of this structure is the oblique view of the sample, usedprincipally for lowering the probe tip to the sample. It also permitsmonitoring of the cantilever tilt with respect to the sample.Additionally, an objective lens is positioned directly above the probeto give a coaxial (on-axis) view of the probe, the sample, and the laserspot on the back of the cantilever. This combination of the on-axis andoblique view is highly advantageous.

A further advantage of the structure of FIG. 12 results from the use ofa conventional motorized zoom lens and its motor encoder toautomatically control the image magnification and field size. After thismotorized zoom lens is calibrated, it is advantageously possible toobtain both optical and scanning force microscopy images of the sampleand accurately correlate features in the two images.

Light from an incandescent bulb 1220 (which is low power/wattage, tominimize thermal heating effects which could cause drift in the system)is condensed by planar convex lens 1202 (which is large enough forproper illumination of the objective aperture) and split by conventionalbeam splitter 1204. A shutter 1206 is aligned to block the path of lightthrough either an on-axis objective lens 120 or an oblique achromat lens1212. (Lens 1212 is a two-element lens to eliminate opticaldistortions.) Lens 1212 may also be an objective lens. Shutter 1206 istranslated by conventional linear motor 1208 to block either light path.For on-axis viewing, light passes through objective lens 120 and isreflected from the back of the cantilever 100 and/or the sample 102.This reflected light follows a path from the beam splitter 1204 tomirror 1210 and down into the conventional camera motorized zoom lens1238 (purchased from Minolta). The image of the probe and/or the sampleis then detected by a conventional CCD camera 1246 for output to, forexample, a video display (not shown). For oblique viewing, the shutter1206 is moved so as to block the light's path through the objective lens120. The light reflects from beam splitter 1204 and mirror 1214, andpasses down through achromat lens 1212. The light then reflects frommirror 1216 onto the probe and/or the sample and is then reflected backalong this same path. The oblique image can then be displayed on-screenin a like manner to the on-axis image.

The optical system is parfocal, such that the achromat and objectivelenses share the same focal plane and such that the focal plane is notaffected by the zoom-lens magnification. The advantage here is theability to change image magnification and still maintain image focus.The objective lens 120 provides, for instance, additional ×10, ×20, or×50 image magnification for the coaxial view and may consist of two orthree such lenses mounted on a rotating turret (not shown) so that themagnification can be adjusted in large steps. The entire optical viewingassembly is rigidly mounted to the base 112. Conventional kinematicmounts (not shown) for the beam splitter 1204 and the mirror 1214 allowthe position of each view to be adjusted independently in roughlyorthogonal directions so as to center the fields of view of eitherproperly on the CCD camera 1246.

A motor assembly 1220 raises or lowers the objective lens assembly 1218to move the sample 102 into the focal point of either lens. (They sharethe same focal plane). A conventional stepper motor 1222 is mounted on avertical slide rail 1230. The motor shaft 1224 is coupled to a pushingscrew 1226 which passes through fixed nut 1228 attached to the base 112.A ball tip on the screw 1226 forms the loading point for the objectivelens assembly. When the motor 1222 turns, the pushing screw 1226 eitherraises or lowers the objective lens assembly 1218. Motor limit switches(not shown) located above and below motor 1222 define its range ofmotion along vertical slide rail 1230. The objective lens assembly 1218is also mounted on a vertical slide rail 1234 to reduce torque. Theachromat lens 1212 and mirror 1216 are mounted on assembly 1218 alongwith the objective lens and can likewise be raised/lowered by the motor1222. Also, oblique and coaxial views share the same focal plane.

The motorized zoom and CCD camera assembly 1236 allow automatic imagemagnification of both a coaxial and an oblique view. The CCD camera 1246is mounted rigidly to the base 112. A collar 1240 fits around themotorized zoom lens 1238 and is clamped to a vertical slide rail 1242which in turn is fixed to the base 112. When the motorized zoom 1238 DCservo motor (not shown) is activated, the motorized zoom assembly 1238extends or contracts while sliding along the rail 1242. A linearpotentiometer 1244 is attached to the motorized zoom lens 1238 andsenses the position of the lens relative to the base so that, withproper calibration, it monitors image magnification and field size.

User Interface for the SPM

The Scanning Probe Microscope (SPM) disclosed herein includes acomputer-based graphical user interface. The typical user uses two mainprograms to acquire and analyze data from the SPM. The first program(called PSI DATA ACQUISITION) is used to control the microscope andcollect data. The second program (called PSI IMAGE PROCESSING ANDANALYSIS) provides data analysis, image processing, and presentation forprint-out. Both programs operate under the commercially availableMicrosoft Windows™ operating system. The user conventionally adjustsvarious parameters by manipulating icons on the screen using a pointingdevice such as a mouse and/or keyboard.

Operating under a windows-like user interface environment is known inthe SPM field. However, several novel features directed to screen layoutand the underlying control processes are disclosed below.

PSI Data Acquisition Screen

The user controls several functions in the PSI Data Acquisition program,and interfaces with this program via (for the most part) one screenwhich operates under the Microsoft Windows operating system.Manipulating screen icons changes program variables, thereby changingthe microscope operating conditions. This screen (or program) is dividedinto several subfunctions.

FIG. 13 shows the screen as the user first sees it. The screen itselfhas several versions, described below. Primary regions of the screen arelabeled in FIG. 13. On the far left, a vertical column of buffer images1302 is shown. Immediately to the right is the Active Window (AW) 1301.An image taken by the SPM will first appear in the AW 1301. To the rightis a digital scope 1304 which shows the scan line trace in real time.Below the digital scope 1304 is the View 1305 used to locate a regionfor the next scan. Scan parameter buttons 1303 beneath the View 1305 areused to set scan parameters. FIG. 13 also shows the optical controlbuttons 1308 located beneath the AW window 1301. “Bulb” button 1308A isused to toggle the light source for the optical viewing assembly on oroff. “Zoom” buttons 1308B control image magnification and field sizeusing the autozoom assembly described earlier. “Focus” buttons 1208C areused to raise or lower the optical view assembly to bring an object intoor out of the focal plane of the lens assembly. “View” buttons 1308D areused to switch between the coaxial and oblique views (i.e., they controlpositioning of the motorized shutter). The far top right of the screencontains several control buttons 1307 which control screen features.Below screen control buttons 1307 are motor control buttons 1306 fordriving the above-described motorized x, y stage and the z stage.

Features of the PSI DATA ACQUISITION screen layout concern the bufferimages 1302, the Active Window 1301, the live line trace provided bydigital scope 1304, and the stage motor control processes which areactivated using motor control buttons 1306 and the optical controlbuttons 1308.

Up to 16 buffered images at a time can be stored in the active(internal) memory of the computer. Four buffer images 1302 can bedisplayed at a time. The buffer scroll buttons 1302A allow the user toscroll through the column of images and display different images. Theuser may save any of these suffered images to a permanent storage deviceby using the mouse or other pointing device to click on the “Save”button below each image. If the user clicks on the “?” button alongsidethe “Save” button, the various parameters pertaining to that image aredisplayed (for instance experimental configuration and image processingparameters). These buffers allow the user to store data collected inreal time in the computer's internal memory instead of in permanentstorage. They also provide an on-screen record of data images for easyreference. The buffers 2002 can contain either newly generated images orimages input from a database. The user can collect several scans fromthe same sample region and save only those needed, thereby making moreefficient use of disk space.

Displaying buffered images on-screen is known. However, previously, thestack of images could not be ported (transferred) between the DataAcquisition and Image Processing programs. The buffered images were lostwhenever a user exited data acquisition mode. The software disclosedherein instead automatically transfers the stack of buffers between thetwo programs. This portability lets the user perform image processing ondata stored in a buffer to determine if an image will be worth saving topermanent storage. Image processing can now be performed on newlyacquired images without first having to save them to a hard disk. Thiscapability gives the user much greater flexibility during dataacquisition.

The AW window 1301 and the transferred buffer images 1302 provide aconstant point of reference as the user switches from the DataAcquisition Program to the Image Processing program. A contrast biascontrol 1301A appears to the left of AW 1201 and is used to adjust thegrey scale of the image. (In a data image, variations in surfacetopography are conventionally represented using a grey scale.) The AW1301 automatically displays the current data image, which can be eitheran optical view obtained using the optical viewing assembly (describedabove) or an SPM scan. A user can also import an image into the AW 1301from a buffer 1302 by clicking on the “Buffer” button 1301B or canretrieve an image from a database using the “Retrieve Image” button1301C. An image that is retrieved from a database is automaticallyloaded into a buffer. If all 16 buffers are full, the oldest bufferedimage is deleted.

The user jumps to the Image Processing program from the Data Acquisitionprogram by clicking on the “Analysis” button 1307A at the top right ofthe screen shown in FIG. 13. The image in the AW 1301 and all 16buffered images 1302, as well as their layout on the screen, are portedto the Image Processing program. Since the left-hand side of the screenappears the same to the user in both programs, the perceived complexityof the system is reduced. Although any prior art multi-taskingenvironment will permit data acquisition and image processingsimultaneously, transferring both the buffered images and the activeimage between the two programs is advantageous over such prior art.

The buttons in scan parameter region 1303 are used conventionally tochange the values of scan parameters such as the scan speed, scandirection, and scan size.

The digital scope 1304 displays the live line trace in the fast scandirection. (The scanner is raster-scanned in the x and y directions. Inthe fast scan direction, the computer collects continually a line a datafor an image, made up of individual pixels. Movement in the slow scandirection positions the scanner for the next line of data.) It is veryuseful to see the live fast scan line trace, for instance to monitor thesensor output, (e.g., the feedback error signal) or surface topographyor feedback error in real time. One prior art product displayed thislive line trace using an analog oscilloscope (instead of a digitalsystem). Prior art systems also use digital scopes. In the presentsystem, the user can activate a digital scope by clicking the “Monitor”button of the screen control buttons 1307.

The present software also has capabilities not found in prior artdigital scopes activated using the “Log” and the “FFT” buttons above thedigital scope 1304. These buttons generate a display of the log of thefeedback error signal and the 1-dimensional FFT (Fast Fourier Transform)of the data in real time, respectively. This is useful, for instance, inSTM, where the tunneling current depends exponentially on thetip-to-sample spacing. Plotting the log of a signal is a usefulcapability, for instance in STM. Since the tunneling current dependsexponentially on the tip distance from the sample, the logarithm of theerror from an STM feedback loop will be linear with the z displacementbetween the tip and the sample and the user can easily obtain usefulquantitative height information from the log plot. The FFT buttonactivates display of the 1-dimensional FFT of the data in real time,which can be plotted as a function of time or space. This capabilitylets the user easily determine the spatial periodicity of a samplesurface, since a peak in the FFT will occur at a frequency correspondingto this spatial periodicity. Additionally, any periodic noise sourceswill be visible as peaks in the FFT time plot. This display thereforeprovides a tool for diagnosing noise problems in the system, e.g.mechanical resonances can be filtered out in image processing. A furtheradvantage of these features is that the user can now take quantitativemeasurements as a scan proceeds, thereby increasing throughput. Theability for the computer to analyze the scan data in real time hasanother advantage besides displaying it graphically to the user. Thecomputer can analyze the scan data by some means (e.g., taking the log,or the FFT in the time domain, measure the height peak-to-peak, etc.)and then use the result of this analysis to change some systemparameters so as to optimize the scanning conditions. For example, anFFT of the data in the frequency domain can indicate when a mechanical(or other type) of resonance in the system is being excited by theexisting scanning conditions. The computer (or controller) can measurethis as a peak in the FFT and then change this parameter (e.g., slow thescan), to reduce its resonance. This use of some functional analysis ofthe data and then the interpretation of the results to optimize thescanning conditions is novel and advantageous.

View 1305 provides a method advantageously to import either an opticalor an SPM image and use this image to assist in controlling themicroscope. View 1305 provides the user with an easy-to-use, andaccurate way to position the next scan automatically, in a particularregion of the sample that has been located using either an optical viewor the SPM. The user activates View 1305 by clicking on the “View”button of the screen control buttons 1307.

To bring in a previously taken SPM image from the AW 1301, the userclicks the “Scanner” button above the View 1305, which ports the imagein the AW 1301 to the View 1305 box. By clicking the “View” button abovethe View 1305, the user can also load an image into View 1305 that hasbeen taken optically using the CCD camera of the optical viewingassembly (described above). The user then locates a new scan region byselecting a feature or region of interest in this image. The userselects this region by positioning a cursor box 1305A around it.Conventionally, the dimensions of the cursor box 1305A can be varied andit can be moved around in the image by dragging the mouse or movinganother pointing device. The user can also move around and zoom in on aparticular portion of the image using scroll buttons. These zoomingbuttons and scroll bars are an additional-advantage over one example ofprior art software, which used only a cursor box. Also, these zoomingtechniques can now be applied to an optical image as well as an SPMscan. Furthermore computer algorithms including pattern recognition canbe applied to images in either the Active Window 1301 or the View 1305which either identify reference marks or otherwise analyze the image soas to permit automated selection and adjustment of the scanningparameter and location of the next scan region.

The cursor box 1305A defines the scan field, including the scan widthand position, for the next scan. If the field of view is defined usingan SPM image, the computer reads the position indicated by the cursorbox 1305A and automatically moves the piezoelectric tube scanner(described above) to that region. If the chosen region is out of therange of the piezoelectric tube scanner (which is often the case whenthe region is defined using an image from the optical view), thecomputer automatically drives the x, y and the z coarse stages toposition the sample for the scan. It is the configuration for the x, yand the z stages using stepper motors and limit switches that makes thisView feature possible. The ability to accurately position the tubescanner is also important and depends directly on the present scansensor arrangement. The computer is able continuously to track the motorposition and thereby retain an accurate position calibration. As aresult, the computer can determine the number of steps necessary to movethe stepper motors for the next scan. With the View feature 1305, theuser can start with a large field of view optical image and take scansthat successively zoom in on a feature of interest until, for instance,the desired resolution is obtained. The capability of this system to leta user graphically define, using a mouse and/or cursors, a scan regionin an optical view and then to position the SPM for this scanautomatically is a substantial advantage.

Along the far right of the screen is the user interface for controllingthe motorized x, y stage and the z stage. The stage motors arecontrolled using a column of motor control buttons 1306. The structureof these stages has been fully described above. The following describesthe processes to control the stage motors which give this SPM systemunique capabilities, by motorizing the three z approach screws. Asdescribed above, motorizing a z coarse stage is known. However, thefollowing control processes relate to the motorization scheme.

The “load” button 1306A raises the probe head up to its upper limits andpushes the x, y stage out from under it for sample loading.

The “center” button 1306B pulls the x, y stage back under the head afterthe sample is loaded.

The “slow approach” 1306C performs a slow z approach until thedeflection sensor registers contact between the probe and the surface ofsample.

The “fast approach” 1306D performs a fast z approach until probe contactwith the sample is registered.

The buttons to control the individual number of steps the motors travelare on a separate screen, activated by pressing the “Move” button at thetop right.

Controlling the stage motors in accordance with the invention allows thesystem to determine the sample height and also to accurately adjustcantilever tilt and pitch while maintaining constant probe height abovethe sample. These modes of control become possible using a motor controlmethod that enables the computer to keep track of motor positionrelative to a fixed zero position which is the same for all z motors.

The sample height (see FIG. 14 showing flow chart) is determined in step1410 by running the z stepper motors to their limit (at zero position)at which the probe head will be parallel to the sample surface.Correction factors may be applied for each system in order to compensatefor manufacturing or other misalignments. Then in step 1412 the motorsare reversed in unison while counting the number of steps taken toapproach and contact the sample surface. The software in step 1414automatically determines the sample height by calculating the number ofsteps to reach the top surface of the scanner less the number of stepsto reach the top surface of the sample. In step 1416, the number ofsteps to reach the top surface of the scanner from the zero position fora scanner of known length L is known, and this value is supplied to step1414. Then the sample height from step 1414 is supplied to step 1418which uses this information to compute a new updated x, y sensitivityparameter for the piezoelectric tube scanner. The prior x, y sensitivityvalue of the scanner is provided from step 1420. (As described above,the x, y sensitivity is an important calibration parameter needed toaccurately determine the lateral motion per unit applied bias thepiezoelectric tube which depends on the sample height.)

In a separate process (see FIG. 13), the cantilever head is tilted usingtilt buttons 1306F, which adjust the angle the cantilever chip makeswith the sample surface. Tilt is adjusted by driving the two z approachscrews positioned at either side of the head the same number of steps inopposite directions. (These two approach screws are set towards thefront of the x, y stage. Refer to FIG. 6C.) It is generally mostdesirable to have the cantilever chip oriented parallel to the surface.For instance, it avoids having a corner of the chip contact the surface.The computer adjusts the tilt so as to maintain the height of thecantilever above the sample. This task is not possible manually and isonly possible under computer-control when the stepwise motion of the1306G like-wise adjust cantilever tilt, but in the perpendiculardirection, as indicated by the graphic appearing above the buttons. Thetwo front z approach screws are raised or lowered relative to the singlerear z approach screw, so as to maintain constant cantilever heightabove the sample.

Clicking on the “Load” button 1306A runs all three z stepper motors backto their limits and drives the y stepper motor to its frontmost limit,thereby raising the head and pushing the x, y coarse stage out fromunder it. Sample loading therefore becomes a simple procedure. Thecapability of the system to determine the sample height and adjustcantilever tilt and pitch over the sample are advantageous featurescontrolled in this portion of the screen.

After the stage is positioned for a scan, the user clicks on the“Control” button 1307C. The motor control buttons 1306 are then replacedby new icons (not shown) and buttons that conventionally control thefeedback parameters.

Two additional advantages relate to computer control of the coaxialoptical view. An optical control process automatically and quicklypositions the probe to within a few microns of the same surface usingthe z coarse stage. This method permits fast movement of the coarse zstage until the probe is within a few microns of the sample surface byactivating the “fast approach” button. Then the “slow approach” buttonslows the z stage to further lower the probe to within the range of thex, y, z fine stage. In addition, an optical control processautomatically determines the slope of a sample surface, for instancewhen the sample is not mounted parallel to the x, y scan plane.Knowledge of the sample slope is used to correct the data image.

This computer control of the coaxial optical view is a significantadvance over the prior art. Previously, the coarse z approach had to bemonitored and controlled manually in order to avoid damaging the probeby crashing it into the surface. In contrast, the present system isfully automatic and significantly shortens the time required to positionthe probe over the sample. The following describes the underlyingcontrol processes of the present system.

As described above, the focal plane of both the coaxial view and theoblique view is adjusted under computer control by a motor mounted via aslide rail to the base 112. (See FIG. 15.) This motor raises and lowersthe optical viewing assembly to bring an object into or out of thisfocal plane, which is common to both views. The optical control processpresets the focal plane of the objective lens 120 a few microns belowthe plane of the probe 100. (This is achieved by focusing on the probe100 and then stepping the motor so as to lower the focal plane below theplane of the probe a known amount.) The z stage and the objective lensassembly 120 are then lowered in unison. Probe 100 thus approaches thesurface of sample 102 and the objective lens assembly 120 lowers so thatits focal plane remains the same distance below the plane of the probe.This focal plane is then brought into coincidence with the sample 102.When it is determined conventionally that the image of the sample 102surface is in focus, the probe will be a few microns (about 2 to 3 μtm)above the surface. The speed of the z coarse stage is then reduced andthe probe is brought to within the range of the tube scanner. Thisadvantageously reduces the time it takes to approach a sample and avoids“crashing” the probe into the surface of the sample. Alternatively theoptical focus is first located on the sample as described above, andthen the probe is rapidly lowered to within a few microns of the samplesurface.

This is achieved by making use of the capability to move the focal planeof the coaxial objective lens under computer control. This process useswell-known software (prior art) to determine if an image is in focus.

As described above, the focal plane of both the coaxial view and theoblique view is adjusted under computer control by a motor mounted via aslide rail to the base 112. (See FIG. 15.) This motor raises and lowersthe optical viewing assembly to bring an object into or out of thisfocal plane, which is common to both views. The optical control processpresets the focal plane of the objective lens 120 a few microns belowthe plane of the probe 100. (This is achieved by focussing on the probe100 and then stepping the motor so as to lower the focal plane below theplane of the probe a known amount.) The z stage and the objective lensassembly 120 are then lowered in unison. Probe 100 thus approaches thesurface of sample 102 and the objective lens assembly 120 lowers so thatits focal plane remains the same distance below the plane of the probe.This focal plane is then brought into coincidence with the sample 102.When it is determined conventionally that the image of the sample 102surface is in focus, the probe will be a few microns (about 2 to 3 μm)above the surface. The speed of the z coarse stage is then reduced andthe probe is brought to within the range of the tube scanner. Thisadvantageously reduces the time it takes to approach a sample and avoids“crashing” the probe into the surface of the sample. Alternatively theoptical focus is first located on the sample as described above, andthen the probe is rapidly lowered to within a few microns of the samplesurface.

A second advantage of computer control of the optical view is that theoptical control process provides a means to automatically determine theslope of a sample surface relative to the x, y scan plane. Such a slopeappears as a uniform tilt in the data image and is not consideredmeaningful topographical data. Knowledge of the sample surface slope isused to correct the data image. The prior art provides means fordetermining the sample slope and subtracting it from the image in eitherreal time or through later image processing. Another use of the tiltinformation obtained from the optical view is to automatically calculatethe tilt of the head (i.e., as described above) so as to bring thecantilever and chip towards the sample surface without the surfacehitting the chip.

In accordance with the present invention, however, the coaxial opticalview is used advantageously to determine the height of the sample atthree different locations. The control process counts the number ofmotor steps required to bring the sample plane into focus at these threelocations. These data are used to calculate the slope of the sample,which can be entered into the x, y and z feedback control loops as apreset parameter, thereby alleviating the need for any real time orpost-imaging slope correction.

PSI Image Processing and Analysis Screens

Clicking on the “Analysis” button 1307A in the PSI DATA ACQUISITIONscreen shown in FIG. 13 transfers program control to the PSI IMAGEPROCESSING AND ANALYSIS screen. As described above, the AW 1301 and allthe buffers 1302 are ported to this program. FIG. 16 shows the PSI IMAGEPROCESSING AND ANALYSIS screen as the user first sees it. The ImageProcessing and Analysis program has three image manipulation modes,entered by clicking on one of the image manipulation mode buttons 1601A.The user enters Analysis mode by clicking the “analysis” button.Analysis mode is used to generate useful quantitative information fromthe data, for instance, measurements of sample roughness or periodicity.Process mode, entered by clicking the “process” button, allows the userto do image processing, such as removing noise from an image or croppingan image. Present mode, entered by clicking the button “present” of theimage manipulation mode buttons 1601A, sets up an image or images forprintout in a desired format, for instance in a multi-image format withcomment fields for each image, or in a 3-D rendered version.

There are several different PSI IMAGE PROCESSING AND ANALYSIS screens,depending on which sub-program the user enters. The Analysis sub-programscreens provide a 1-dimensional OFT with variable high and low passfilters which are adjusted using a mouse, and also a 2-dimensional FFTwhich first operates on a reduced data set for increased processingspeed. The sub-program called Present screens use a graphic icon to showthe effect of varying 3-dimensional rendering parameters, such as theposition of an artificial light source.

FIG. 17 shows the screen as the user sees it after entering the Lineanalysis mode of the Analysis subprogram. The AW 1701 is shown,displaying the line analysis of the image it contains. There are twoimportant differences between the 1-dimensional FFT 1704 here and the1-dimensional FFT of the digital scope 1304 in the Data Acquisitionprogram. Since the digital scope 1704 shows the live line trace, the FFTcan only be performed in the fast scan direction. In Line Analysis mode,however, the user can choose any arbitrary line, including a shortsegment, on which to perform a 1-dimensional FFT. This gives the usergreater flexibility for data analysis since, for instance, periodicitiesin directions other than the scan direction can be examined. The seconddifference concerns a variable bandpass filter.

The user can choose a line of data to analyze in several ways. The linestyle and placement of the end points are chosen using the line choicebuttons 1702 to the right of the AW 7101. The chosen line (essentiallythe plot of the z intensity along the line) is displayed in unfilteredline box 1703 below the AW, and the 1-dimensional FFT of this line isautomatically displayed in filtered line box 1704. The user can chooseto have specific aspects of the line computed and automaticallydisplayed in tabular form in table 1706. These quantitative measurementscan include, for instance, surface roughness and peak-to-peak height.The user may choose more than one line at a time.

The user can filter the line display in box 1703 to reveal or eliminatevarious periodicities by adjusting the values of a band pass filter. Thevalues of the filter are indicated by the position of cursor arrows 1705for filtering, which point to the filtered line in the filtered line box1704. The left-most arrow 1705 is a high pass filter and the right-mostarrow 1705 is a low pass filter. The user adjusts the position ofcursors 1705 by clicking on them and dragging them along the line usingthe mouse. Moving cursors 1705 eliminates various frequency componentsfrom the filtered line box 2304.

The filters indicated by cursor arrows 1705 are used to eliminate one ofthe spectral peaks of the FFT. When the cursor arrows 1705 are moved,the computer calculates the reverse FFT in real time and this isdisplayed in the window. The user can therefore see the effect of thefiltering immediately. This filtering uses cursors 1705 to adjust thefiltering parameters and which displays the results of the calculationin real time, in both a graphical display and a tabular format, makingline analysis intuitive and easy to use.

In Filtering mode (see FIG. 17), the user can use a 2-dimensional filterto take the 2-dimensional FFT of an image. The values of the high andlow pass filters for both the x and y directions can be changed byeither typing in new values or using scroll bars. This softwareadvantageously calculates the 2-dimensional FFT using a reduced data setsuch as a neighborhood of contiguous pixels. By using one quarter of theimage, for instance, the calculation proceeds much faster. After theuser has optimized filtering parameters, these can then be applied tothe entire data image.

FIG. 18 shows the 3-dimensional Rendering screen. The primary featureshown is use of a graphic to show the effect of varying 3-dimensionalrendering parameters such as the position of an artificial light source.This screen displays the buffered images 1302 and the AW 1301. Whicheverimage is brought into the AW 1301 will be the one rendered in a3-dimensional perspective in region 1803. This operation involvespositioning an artificial light source and varying the viewing angle ofthe image, among other variables, to enhance edge perspective and createthe illusion of a 3-dimensional perspective of the surface.

Although the prior art lets the user vary these 3-dimensional renderingparameters, the prior art process of optimizing them to create the best3-dimensional rendering is tedious and non-intuitive. In the prior art,the user must choose numerical values for these parameters. The computerthen calculates and draws the resulting image, a process which takesseveral seconds. The user then decides if another iteration isnecessary.

FIG. 18 shows the present method for varying these parameters. Thesoftware uses a dedicated graphic 1801 to show the user in real time theeffect of varying these 3-dimensional rendering parameters, and lets theuser optimize these parameters visually before applying them to the dataimage. The iteration process required to generate the final image is nowsignificantly shorter. In addition, since the perspective view of thegraphic changes in real time, the user can immediately see the effect ofchanging a parameter. The process is therefore much more intuitive andno longer requires dealing with numerical values. Any suitable graphiccan be used for this purpose, including a portion of the real data image(for instance, a piece of the image with lower resolution, with fewerscan lines or pixels drawn for faster computation times).

The graphic 1801 is an artificial structure having simple geometries,hence greatly speeding computation and drawing time. The user changesthe 3-dimensional rendering parameters using the 3-D parameter scrollbars 1802. The perspective view of graphic 1801 is updated in real timeto show the effect of changing each parameter. When satisfied with thisview 1801, the user clicks on the done button 1804, thereby applyingthese optimized parameters to the real data image displayed in the AW1301. This image rendered in a 3-dimensional perspective is shown in 3-Dimage box 1803. The user can change the resolution of the final imageand the color display by clicking on the resolution and color buttons1805 at the bottom right of the screen.

It is to be understood that implementation of the above-described screenimages and control methods may be achieved in many different ways interms of computer programming, and implementation of such computerprograms is well within the abilities of one of ordinary skill in theart, given the above description.

The above disclosure is illustrative and not limiting; furthermodifications will be apparent to one of ordinary skill in the art inlight of this disclosure and the appended claims.

We claim:
 1. A microscope providing to a viewing device both an obliqueand an on-axis view of a sample, comprising: a light source providinglight along an axis; a support for the sample located on the axis; aviewing device located to receive an on-axis view of the sample when thesample is on the support; a reflector located adjacent to the supportfor providing to the viewing device a view of the sample obliquelyrelative to the axis; and at least one shutter for alternatively: 1)interrupting the on-axis view from reaching the viewing device, andallowing the oblique view from the reflector to reach the viewing deviceor 2) interrupting the oblique view from the reflector from reaching theviewing device.
 2. The device of claim 1, wherein the viewing deviceincludes: an auto-zoom lens; a camera for receiving an image from theauto-zoom lens; and a controller for the auto-zoom lens.
 3. The deviceof claim 1, wherein the on-axis view is focused and magnified onto theviewing device by a first lens movable with respect to the axis, and theoblique view is focused by a second movable lens onto the viewingdevice.
 4. The device of claim 3, wherein the first and second lens aremovable along the axis under motor control.
 5. The device of claim 1,further comprising: a scanning probe microscope having a display; meansfor displaying a scanning probe image on the display; and means fordisplaying an image from the viewing device on the display.
 6. A methodfor operating a microscope providing both an on-axis and oblique view ofa sample to a viewing device, comprising the steps of: providing areflector for providing oblique light from the sample, the reflectorlocated adjacent to the sample and oblique to an axis of incident lightonto the sample; and alternatively: 1) interrupting with a shutter theincident light from the sample back along the axis and allowing theoblique light from the sample to reach the viewing device and 2)interrupting the oblique light from the sample to the reflector fromreaching the viewing device.